On board a space vehicle such as a satellite there are numerous pieces of electronic equipment such as amplifiers, receivers, filters, etc. These pieces of equipment are often provided redundantly for reasons of reliability, and they may belong, for example, to a system for relaying television or telephone signals by satellite, or to systems for performing service functions on board a satellite (on-board management, attitude control, power supply, etc.).
When a satellite is launched, a nominal operating configuration is selected, i.e. various pieces of equipment are selected to perform service functions, some channels are selected to carry telephone signals, and some channels to carry television signals. During the lifetime of the satellite, and in particular for commercial reasons, it may be that its configuration needs to be modified. In order to reconfigure equipment to satisfy requirements, control and monitoring stations on the ground send remote control signals (RC) over a radio link to a receiver on board the satellite, and the signals are applied to a digital central control unit (CU) constituted by a unit referred to as control terminal unit (CTU) for processing these signals together with a plurality of remote terminal units (RTUs) for applying these signals to the various pieces of equipment. The RC signals may also serve to select amongst redundant equipment which pieces will actually be active, in particular amongst systems that perform service functions on board the satellite. The RC signals thus serve to control and manage the operation of all of the on-board electronic equipment.
It is always desirable to perform tests for inspection purposes, either to verify that the RC signals have been properly executed, or to detect from the ground that possible breakdowns have occurred that run the risk of harming proper operation of the satellite or of disturbing the signals it relays. Various pieces of equipment therefore send telemetry signals (TM) to the central unit, which signals are forwarded to the ground by appropriate transmitters on board the satellite and in communication with the central unit. The TM signals may be transmitted either in response to RC signals, or they may be transmitted systematically so as to enable the state of on-board equipment to be monitored continuously.
The TM and RC signals are transmitted between the central unit and the various pieces of equipment in conventional manner by using wire links made up into cables; considered as a whole, these wire links for transmitting remote control and telemetry signals is referred to as the “TM-RC harness”.
In addition to requiring these remote control and telemetry and acquisition signals RC and TM to be transmitted, the payload equipment and the platform equipment of satellites also require frequency or time reference (clock) signals, electrical power supply, etc.
Each type of signal is conveyed by a dedicated and specialized network based on wire links. Like the TM-RC harness for TM-RC service signals, each network requires a specific harness to be designed, made, and installed.
However, these harnesses are expensive, heavy, and different for each satellite. The time they require for integration is long: this includes verifying each harness wire by wire, verifying each connector contact by connector, monitoring each signal whenever a piece of equipment is mounted, and verifying electromagnetic compatibility.
Known solutions for reducing the mass of a harness and the number of links it involves exist in the following forms:                for remote control and telemetry signals RC and TM, one known solution consists in using digital buses for conveying the various digitized signals going to or from the various pieces of equipment, said signals being time division multiplex. However, that solution remains limited and, for example, it does not cope with the need for frequency references (local radio frequency (RF) oscillators) or time references (clocks or synchronization pulses), for example;        the frequency references or local oscillators (LOs) and ultra-stable oscillators (USOs) are grouped together within specialized coaxial cable networks. In addition to their significant mass, those networks electrically interconnect pieces of microwave equipment that are highly sensitive, and that leads to severe problems of electromagnetic compatibility between pieces of equipment.        